The present invention relates to a heat-cooking apparatus incorporating an infrared detecting system.
In a heat-cooking apparatus such as an electronic oven, it is highly desirable to automatically control the heat source in accordance with information concerning the progress of the cooking thereby automatically achieving good cooking.
To this end, there have been proposed and used various types of controllers for heat-cooking apparatuses. For instance, it has been attempted to detect the temperature of the heat-cooked material directly by inserting a temperature sensor into the material. It has been also proposed to control the heat source by detection of the temperature or humidity of the atmosphere within the oven cavity which changes as vapor is generated from the material being cooked.
The use of a temperature sensor insertable into the material being cooked permits direct detection of the temperature but on the other hand poses various problems as follows. Namely, this type of sensor can provide the temperature information of only a specific portion of the material where the sensor is inserted. In addition, this sensor cannot be used in the defreezing of material to be cooked because it cannot be inserted into hard frozen material.
The control device relying upon the detection of temperature or humidity of the atmosphere in the oven cavity also poses various problems such as indirect and, hence, inacurate detection of the temperature of the material being cooked which causes a large fluctuation in the quality of cooking particularly in the case of short-time cooking and so forth.
Thus, the control devices heretofore proposed are still unsatisfactory in that they cannot fully meet the demand for good and automatic cooking with heat-cooking apparatus.
On the other hand, the current progress of technology has accomplished a remarkable improvement in the material and processes for producing sensors including infrared sensor. The infrared sensor is a kind of non-contacting type sensors which makes use of the natural phenomenon that a body having a temperature above absolute zero (0.degree. K.) radiates infrared energy from its surface at a rate which is related to the temperature thereof.
Partly because of the demand for better automatic cooking, and partly because of above-explained development of non-contacting type sensors, particularly the infrared sensors, it has become possible to apply the infrared sensor to various machines and equipment for daily life, e.g. the heat-cooking apparatus.
In applying the infrared sensor to heatcooking apparatus, it is necessary that the sensor operate with low infrared energy corresponding to a temperature ranging between -20.degree. to -10.degree. C. the temperature of frozen foodstuffs) and 120.degree. to 180.degree. C. the temperature at which foodstuffs are slightly burnt or scorched). For reference, the intensity I of infrared rays is proportional to .mu..times.T.sup.4, where .mu. and T represent, respectively, the radiation rate and the absolute temperature of the object. In addition, there is a problem of induction noise and noise caused by microwave radiation from the heat source (heater or high-frequency wave generator) of the heat-cooking apparatus. Although the wave treated by the infrared sensor has a relatively large wavelength of the range from several to several tens of microns (.mu.m), the infrared sensor inevitably makes use of an optic system. Thus, there also is a problem concerning contamination of the optical system.